The machining of pipe ends of very long and out-of-round or similarly deformed workpieces, for example, pipes used in the oil industry (e.g. for drill strings), with machine tools in which the workpiece rotates while the tool is stationary, is generally associated with disadvantages because the workpieces tend to vibrate under rotation, and such vibration is difficult to control.
Accordingly, machine tools have been developed in which the workpiece is stationary and the tool, for example a lathe cutter of machining steel, is revolved or rotated about the workpiece.
Rotating toolheads are used for such machining and they are equipped in the manner of chuck assemblies in which the chuck jaws are replaced by radially movable head carriages to which the respective toolholder can be secured.
Toolheads can include only a single toolholder, but toolheads which utilize several toolholders are also known, and the radial movement of corresponding toolholders should be synchronized in these.
One known machine has a lengthy head carriage which is movable along a line which is diagonally disposed with respect to the toolhead, and the head carriage is equipped with a tool at each of its ends. The toolholders engage over the workpiece in the manner of forks. When the head carriage is moved in upward direction, the lower workpiece is engaged. When the head carriage is moved downwardly, the upper cutter steel is operative.
The kinematic configuration of the toolhead is complex because a radial advancing motion has to be imparted to the rotating component. The mechanism for this includes an axially movable rod which is arranged within the hollow main spindle. The rod cooperates with adjustment wedges which effect the radial movement of the head carriage. Such an arrangement is quite sufficient for simple machine tools. It is, however, of detriment that the hollow main spindle cannot be used for a rotating center or other alignment spindle or positioning device and it cannot be used for the supply of a cooling medium. Only a single adjustment or motion to the cutting tool (advance) can be transmitted for a synchronized group of tools.